The aims of the project are 1) To expand information on the disease-producing potential of JC virus and BK virus in extraneural tissues and on sites of latent infection by these viruses. Children with urinary tract infections and immunosuppressed persons with interstitial pneumonia will be studied; 2) To continue development of information about the role of JC virus in progressive multifocal leukoencephalopathy. Virus isolated from diseased brain tissue will be compared with virus from other sources. Viral proteins will be studied; 3) To isolate and characterize new human polyomaviruses; 4) To continue development of information about the oncogenicity of JCV.